Electric heating pad



oct. 22, 1935. w w, DE LANEY E1- AL 2,018,512

ELECTRI C HEATING PAD Filed June 30, 1931 3 Sheets-Sheet 1 Zz zz Y ZI 2]/ Z0 zo zo lill/lill]llllllllnll/Ililna 'nudi/1) anlillnllllallilla/I/ Jwuentowlaura MJQJLW @www www Oefu 22, 1935.

w. w. DE LANEY r AL 2,018,512

ELECTRIC HEATING PAD Filed June 30, 1931 3 Sheets-Sheet 2' Oct. 22, 1935A. w w, DE LANEY Er AL 2,018,512

ELECTRIC HEATING PAD 3 Sheets-Sheet 3 Filed June 30, 1931 ,Lunar-RM mentado@ .193s n l PATENT OFFICE momo HEATING Pan.

Wallace W. De Laney, New Haven, and Walter B..

Weeks. Hamden, Conn., assignors to The Seamleas Haven, Conn.

Rubber Company, Incorporated,

New

Application June so, 1931, serial No. 547,910

z5 claims. (o1. 21a- 46) 'Ihis invention relates to electric heating pads auch as used in homes and hospitals.

One of the objects of our invention is to provide a padn having a casing of rubber or like 6 plastic insulating material so that it is moisture proof and can be used with damp cloths for providing a `moist heat and can be easily cleansed and kept in a sanitary condition, and which is in the form of a sheet which isvery thin and has l maximum flexibility so that it may be readily conformed, if desired, to the body, head or limbs of the user in order to obtain the most eillcient results. Notwithstanding the provision of these advantages we aim to furnish, in addition, a pad l having sumcient heating capacity for the purposes in view, in which the heating coil or coils are under proper thermostat control so that the appliance will be entirely safe to use, and to embody these features in a structure which can be manufactured readily and at comparatively low cost.

To these and other ends, the invention consists in the novel features and combinations of parts to be hereinafter described and claimed.

In the accompanying drawings:

Fig. 1 is a face view of a heating pad constructed in accordance with our invention;

Fig. 2 is a view of the opposite face of the pad with the conductor cord broken away;

Fig. 3 is an edge view;

Fig. 4 is a section enlarged beyond actual size and taken on line 4 4 of Fig. 2;

Fig. 5 is a sectional view taken on line 5-5-of F18 2. Fig. 6 is a diagrammatic view of the electrical circuits which may be used;

Fig. 7 is a fragmentary plan view of the pad, showing some of the parts illustrated in Fig. 4; Fig. 8 isa fragmentary sectional view of the cord-attached end of the pad;

Fig. 9 is a plan view of a partially completed pad having a somewhat different arrangement of heating circuit;

Fig. 10 is a detail of one of the rubber fillers used' -in lbuilding up the thermostat enclosing structures; f

Fig-111s an enlarged section on line Ii-II of Fig. 9, illustrating the process of making the Flgs12 and 13 are detail views of the cored resistance elements auch 'as used in the form illustrated in Figs. 1, 2 and'3;

` 14 is a sectional view of a thermostat, and u Fig. 15 vis a fragmentary longitudinal section,

similar to Fig. 4, but showing a modified construction.

In Figs. l, 2 and 3 we have shown the preferred exterior shape or configuration of our heating pad, which is in the form of an elongated g approximatelyelliptical sheet 20 of plastic electrical insulating material, preferably rubber. This sheet which may conveniently be about twelve or thirteen inches long, is characterized by its thinness and great flexibility. As a result 10 of the improvements hereinafter described, we can successfully construct rubber pads having a thickness of one-eighth of an inch or thereabouts in most of their area, and this is a feature of considerable advantage because it provides a 15 structure which can be readily flexed so as to conform the pad to the body or head of the user, or so as to wrap or fold it about an arm or leg.

At one end of the pad is attached at 2l a moisture proof conductor cord 22, leading to an zo ordinary temperature-controlling switch 23, and from the switch 23 the customary heater cord 24 leads to an attaching plug 25.

'I'he covering 26 of the conductor 22, which is preferably made of rubber, is increased in thick- 26 ness adjacent the end of the pad, as shown at 21 in Fig. 8. The thickened wall 21 of the conductor is integrally joined with the body or sheet portion of the pad.

In the form shown in Figs. 1, 2 and 3, the 90 rubber body or sheet contains heating resistances which are in the form of wire helices embedded centrally in the sheet and extending across the same in spaced parallel relation substantially throughout the length of the sheet. The coils may be of round cross-section, as shown, or they may be of elliptical or other suitable cross-section. Fig. 6 shows diagrammatically the circuits which we prefer to employ in a pad whose switch is adjustable to give three different degrees of 40 heat, namely, low, medium and high. In this view, the dotted line 28 indicates the "medium heat resistor, which can be appropriately constituted by a wire having its turns of relatively small diameter and considerably spaced from 48 each other, as shown in Fig. 12. In Fig. 6, 29 indicates a low heat resistor such as shown in Fig. 13, and it will be observed that in this case the turns of the wire are of a greater diameter and are more closely spaced so that when a given so length of the wire is traversed by the current. less heat will be generated than in the case of the medium heat wire. It will be observed from Fig. 6 that the medium heat wire 28 passes from one of the three conductor terminals in a num- 56 sol ' gently sloping sides. 45.

ber of reaches or spaced parallel portions to a thermostat 38, located near the remote end of the pad, and continues on from this thermostat back to the thermostat 3i, located near the opposite end of thepad. On the other hand. the low heat wire 28 leads from another terminal of the conductor, by a number of spaced parallel portions, to the opposite end of the pad, then back toward the first end, where it is connected to the thermostat 3|. From the thermostat 8i the resistors 28 and 28 lead back in multiple connection to the third terminal of the conductor. 'I'he switch 23 is adapted to cut in either the low heat circuit or the medium heat circuit, or both, and in the latter case the adjustment is for high heat.

A suitable thermostat is shown indetail in Fig. 14. Such a thermostat has a steel body 32 in the form of a block having an inner cavity 33, covered by a steel lid or cap 35, which conforms closely to the body and may be conveniently soldered to the body. The cap 35 when placed in position effectively seals the hollow block against the entrance of any exterior substance, such as rubber. Anchored in the block 32 and projecting into the cavity 33 is an ordinary bi-metallic thermostat bar 36 adapted to cooperate in the usual way with a contact member 31, insulated from the block by insulation 38, and having a. pro- Jecting portion to which a resistor element or wire may be readily connected as by soldering. 'I'hese thermostats are embedded in our sheet rubber pad body, and in the form shown in Figs. 1, 2 and 3, Where it is desired to use a minimum amount of rubber in the pad body consistent with satisfactory results, those portions of the body which contain the thermostats 30 and 3| are somewhat raised from the plane of the sheet on one side, so as to create projecting portions 39 in the nature of bosses, which securely enclose and protect the thermostat devices. These bosses are preferably of generally elliptical shape, as shown in the drawings, and have fiat tops and In other words, this construction provides a thermostat-enclosing portion at one face of the sheet, which merges into the remainder of the sheet and so no abrupt shoulders or projections are presented. As shown in Fig. 4, the thermostat 30, which is of rectangular cross-section and somewhat elongated, lies on its side in a correspondingly shaped chamber in the body of the sheet between one of the medium heat resistors 28 and one of the low heat resistors 28 which in this particular case are embedded in the rubber in a plane approximately in line with the lower face of the thermostat body. Below the thermostat and underlying the resistors within the thermostat enclosing boss is a piece of vrubberized fabric 48, em-

' bedded in the rubber and having its fabric face lowermost. This piece of fabric may be of substantially square shape but its shape is not particularly important. A similar rubberized fabric piece 4i overlies the thermostat in the boss or protuberance 39, being embedded in the rubber adjacent the upper face of the rubber sheet or body, as viewed in Fig. 4, and at its margins this fabric piece 4i, which has its fabric face uppermost, is inclined downwardly so as to conform to and follow the inclined marginal portion of the boss.

The conductor cord 22 is, in this form, provided with three separate conductors and each conductor is enclosed in a rubber covering 42, as shown in Fig. 8. If desired, each conductor may be covered with an asbestos covering in addition to the rubber covering 42. Between these conductors a filler of cotton orthe like is placed. Over this illler is a suitable braid 44,

such as a cotton braid. The rubber covering s or neck 21, which is of considerable thickness as above described, extends substantially beyond one end of the p ad body and to this portion the thinner rubber wall portion 2l o! the conductor cord is integrally Joined. As a result, it is 10 possible with the particular pad illustrated, to project the pad body into water and also that portion of the conductor extending up to the switch, without any moisture getting into the pad or the conductor cord leading thereto. 1I

In Fig. 9 we have shown a modified form oi heating pad in which the body is constructed substantially in the manner previously described but in which a single resistor is employed. This resistor may, for example, be of the kind shown I) in Fig. 12, that is, it may be constituted by a resistor 28 similar to the resistor 28 previously described. In this case, the resistor is led back and forth in reaches or stretches which are fairly close to each other and extend substantially ll from one end of the pad to the other. Thermostats 38 and 3i similar to those previously described are used in this case, one of these being interposed in the circuit near one end of the pad and the other being interposed in the circuit near the other end. It will be understood that in this case the two thermostats are used in series so that one constitutes a check upon the other. It will further be understood that various alternative circuit arrangements may be employed as desired, those shown herein being merely by way of example. It will be obvious. of course, that in the example shown in Fig. 9, the cord or cable attached to the pad is a twoconductor cord. It is, however, connected to the so pad in substantially the same manner as the cord or cable 22.

In manufacturing a pad such as we have described, the procedure is substantially as follows.

Two sheets of unvulcanized rubber conforming 4gv generally to the desired final contour, which may have a thickness of, say, one-sixteenth of an inch, are provided. Upon the face of one of these sheets, resistor and thermostat parts are assembled in the manner generally indicated in Fig. 9. lo Where the single resistor circuit is to be employed, the wire is placed upon the upper surface of the sheet in parallel lines or reaches substantially as shown in Fig. 9. First, however, the pieces 40 of rubberized fabric are placed in position and the resistor wire has certain of its reaches placed across these pieces. When the resistor wire is placed in position uponA the sheet it is provided with a core. We prefer to make the core of rubber, either uncured or only parso tially cured, the fine resistor wire being wound helically upon the rubber core. In practice, the rubber core for the resistor 28, which core is indicated at 45 in Fig. 12, may have a diameter of, say, three sixty-fourths of an inch. The reas sistor 29 used in the form of pad shownin Fig. 1 has a similar rubber core 45' (Fig. 13), which may have a diameter of, say, one-sixteenth oi' an inch. The wire itself may be No. 32 B 8: S gauge in each case. The helically wound wire 'l0 having its interior rubber core may be arranged in proper formation upon a suitable board or the like, and may have naphtha applied to it so that upon pressing the rubber sheet down upon the wire the sheet will pick up the wire and there- 75 after the wire-covered face of the sheet can be arranged uppermost, as shown in Fig. 9. 'Ihe thermostats are then interpolated in the circuit and placed on the fabric pieces Il, and around each of the thermostat's two rubber pieces or fillers t are placed, these fillers having rectangular openings l1, shaped to conform closely to the thermostat body. Then, upon each uppermost rubber piece 48 is laid a fabric piece 4I,

with its fabric face uppermost. The conducting cord. which at ,this time is already supplied with a rubber covering extending substantially to its inner end, is laid upon the upper surface of the sheet near one end and its terminals spread apart and connected with the resistor or resistors. as the ease may be, and the cord is temporarily held in place by means such as arubber strip l'l'A extending over its rubber cover and cemented to the upper face of the sheet.

The lower sheet structure having been thus prepared and carrying on its upper face the various parts as shown, for example, in Figs. 9 and ll, the upper rubber sheet, which is indicated by the dotted lines at Il in Fig. 1l, is laid upon the lower sheet. The article is then placed in a metal mold, such as required to form a body of the shape shown, an additional amount of rubber being placed on a portion of the conductor cord which projects out, say, a few inches beyond the end of the sheet. The mold and its contents are then heated in the usual manner and the two plates of the mold pressed together under very heavy pressure so as to produce the completed wire-containing sheet having a neck portion enclosing and integrally joined to the rubber-covered conductor cord. By molding rubber around the rubber-covered conductorthe pad is provided with a relatively thick neck portion which gives great strength to the connection between the cord and the pad and enables it to withstand the twisting and bending strains to which it is subjected.

In the molding operation the material of the sheets and the material of the resistor core or cores are flowed together into an integral structure and the cores extend between the turnsgof the coils and are joined in one piece with the surrounding body of rubber.

In molding the bocLv of the pad, a very high pressure is used, for example, 2000 pounds to the square inch. It is, therefore, of the utmost importancelthat this pressure be prevented from destroying or injuring any of the metallic parts "used in the construction of the pad. We have been able to meet the requirements by providing a rugged thermostat block which is constructed of steel so as to withstand this high pressure, and which additionally is so constructed as to prevent the rubber from entering the interior of the thermostat during the molding operation. Ordinarily, the molding pressure would be sumcient to flow the rubber into'the interior thermostat chamber and thereby render the thermostat inoperative, but in our construction the thermostat block is sealed against the entrance y of the rubber and the greater the pressure exerted in the molding operation the closer will be the fit between the cap portion of the thermostat and the body thereof.

In some cases we find it desirable in assembling the parts to place one of the rubber pieces 46 in position on each underlying piece of rubberized fabric before the resistance wires are placed in position on the lower sheet, and to run the wires over the upper surface of the piece It instead of between this piece and the piece 40, as shown in Fig. l1. The thermostat will then be connected to the wires and laid in its recess or pocket in the piece lt. and the remaining steps will be as previously described. It will be understood that if l we proceed in this manner some or all of the reaches of coiled wire in the thickened portion of the pad adjacent each thermostat will be located approximately centrally of the thickened portion instead of to one side of the center, as shown l in Fig. 4.

In Fig. we have shown a modified form of pad having a similar resistor and thermostat arrangement to that described in connection with the form of Fig. 1, but wherein the body of the pad is of increased thickness. This particular form of pad is suitable for hospital use, where a somewhat more rugged type of construction is desirable, and in this case the thermostats are located substantially in the median plane of the body instead of being offset from such plane, as in the form first described.

During the molding of the parts as described. vulcanization takes place in the usual manner.

It will be observed that in our heating pad as herein described the resistor structure comprises a plurality of fine coils of helical formation, which coils are of substantially round cross-section, preferably with their longest reaches or stretches disposed transversely to the lengthwise axis of the pad body and running substantially parallel to each other. 'Ihese coils are not only embedded in the body of thevpad, but in the completed pad are provided with interior rubber cores which give them effective internal support and properly space the turns for insulation purposes. such ruby ber cores in the completed article being integral with the outer body of rubber which encloses the coils.

Various changes may be made in the details of 60 the construction and in the process of making the pad without departing from the scope of our invention as defined in the claims.

What we claim is:

1. A heating pad comprising a plastic sheet. a resistor structure embedded in the sheet and comprising a hollow coil, and a plastic core within thecoil, said coil being of helical formation and said plastic core being integrally joined with the body of the sheet.

2. An electric heating pad comprising a rubber sheet and a plurality of hollow resistor coils embedded in the sheet and having rubber in the interior thereof integrally joined with the surrounding rubber of the sheet, said coils being of substantially round cross-section.

3. A heating pad comprising a thin elongated rubber sheet, heating coils disposed substantially parallel to each other transversely to the longitudinal axis of the sheet and embedded in the 5 sheet, each coil being of `substantially round crosssection and formed as a helix and having its axis disposed substantially in the plane of the sheet, and rubber cores in said coils extendingout of the same between the turns and integrally joined 55 with the surrounding material of the sheet.

4. A heating pad comprising a thin elongated rubber sheet, heating coils disposed substantially parallel to each other transversely to the longitudinal axis of the sheet and embedded in the sheet, each coil being of substantially round crosssection and formed as a helix and having its axis disposed substantially in the plane of the sheet, rubber cores in said coils extending out of the same between the turns and integrally joined 'II with the surrounding material of the sheet, and a thermostat embedded in the sheet andconnected with one of said coils.

5. A heating pad comprising a rubber sheet; a resistor embedded therein, and a thermostat embedded in the sheet and connected to the resistor, said sheet having a boss at one face forming a part of the enclosing structure of said thermostat, said thermostat being interposed between the outer face of said boss and the outer face of the sheet in that portion where the boss is located.

6. A heating pad comprising a thin rubber sheet, a resistor embedded therein comprising a plurality of helices of fine wire disposed substantially parallel to each other, a thermostat emv bedded in the sheet and connected to the resistor, a rubber neck integral with the sheet at one end thereof, a conductor extending inwardly through said neck and enclosed thereby and connected with said resistor, and a rubber covering for an external portion of said conductor integrally joined with said rubber neck, said neck having a wall of greater thickness than said covering and gradually merging with said covering.

7. An electric heating pad comprising a sheet of plastic electrical insulating material, a helical resistor coil embedded in the sheet, and a core of plastic electrical insulating material interiorly supporting the coil and integrally joined with the material of the sheet in the intervals between the turns of the coil.

8. A heating pad comprising a rubber sheet, a resistor wire embedded in the sheet, and a thermostat embedded in the sheet in the plane of the resistor wire and connected with the resistor wire, said thermostat comprising a small hollow rectangular block having a thermostat bar therein, and a cover plate extending along one side of the block and sealing the same against the inflow of rubber.

9. A heating pad comprising an elastic sheet, a resistor coil embedded in the sheet and having a plurality of convolutions, and a thermostat in one of said convolutions embedded in the sheet comprising a hollow rectangular block having a recess therein at one side thereof, a thermostat bar in said recess, and a cap plate at the side of the block closing said recess.

l0. A heating pad comprising a rubber sheet,

` a resistor wire embedded in the sheet and thermostats embedded in the sheet and connected with the resistor wire, said sheet having bosses projecting from the face thereof in the regions where the thermostats are located.

1l. A heating pad comprising a rubber sheet, a resistor wire arranged in convolutions extending transversely of the sheet, and thermostats connected with said resistor wire and embedded in the sheet at points located toward the respective ends of the sheet, said sheet being thickened in those regions where said thermostats are located.

12. A heating pad comprising a rubber sheet, a resistor embedded in said sheet in convolutions extending transversely thereof and comprising sections arranged to create different degrees of heat, and thermostats connected with the resistor and embedded in the sheet on opposite sides of the center thereof, said sheet having tapering bosses projecting from the face thereof inthose locations where the thermostats are embedded.

13. A heating pad comprising a plastic sheet, a resistor wire embeddedln the sheet and arranged n convolutions, therein, and a thermostat embedded in the sheet and connected with the resistor wire, said sheet having a boss projecting from one face thereof in the location in which said thermostat is embedded.

14. A4 heating padcomprising a plastic sheet, '5 a resistor wire embedded in the sheet and nrranged in convolutions therein, and a thermostat embedded in the sheet and connected with the resistor wire, said sheet having a boss projecting from one face thereof in the location in 10 which said thermostat is embedded, said boss having a slanting side surface.

15. In a heating pad, the combination with a pad body of rubber, of a resistor embedded in the body and arranged in convolutions therein, and 1gl a pair of thermostats embedded in the body in diiferent locations, one thermostat being located toward one end of the pad and the other toward the opposite end, said resistor comprising a heating section connected with one thermostat Only. lol another heating section of diii'erent degree connected with both thermostats, and a duplex return section leading out of the pad from one of the thermostats.

16. A heating pad comprising a thin elastic g5' sheet, a resistor embedded in said sheet and comprising resistor wires passing back and forth in convolutions arranged transversely of the sheet, and thermostats connected with the wires and embedded in the sheet and located respectively 30 toward opposite ends of the sheet, said thermostats being substantially in the plane of said convolutions and located between certain convolutions and said sheet having bosses projecting from the face thereof in the regions where said u thermostats are located.

17. A heating pad comprising a plastic sheet,

a resistor wire embedded in the sheet and arranged in convolutions therein, and a thermostat embedded in the sheet andconnected with the o resistor wire, said sheet having a boss projecting from one face thereof and the thermostat being located partly in the boss and partly in that portion of the sheet from which the boss projects.

18. A heating pad comprising a plastic sheet, 5. a resistor wire embedded in the sheet, and a thermostat embedded in the sheet and connected with the resistor wire, said sheet having a boss projecting from one face thereof and disposed over the thermostat, said boss having a ilat outer face with a curved margin and a slanting side surface.

' 19. In a heating pad, a pad body of plastic material in the form of a sheet, a resistor embedded in the sheet and arranged in convolutions therein, said resistor comprising sections adapted to create different degrees of heat, thermostats embedded in the sheet and connected with the resistor, said thermostats being located on opposite sides of the center of the longitudinal median line of the sheet, one being located toward but somewhat spaced from one end of the pad and the other being located toward but somewhat spaced from the opposite end of the pad, said sheet having bosses projecting from the face thereof in the regions in which said thermostats are embedded.

20. A heating pad comprising a thin sheet of flexible rubber, a resistor embedded in the sheet and arranged in convolutions extending transversely thereof, a thermostat connected with the resistor-.and embedded in the sheet within the lines thereof in a location intermediate the center of the sheet and one end thereof, a second thermostat connected to the resistor and embed- `section extending substantially from the conducded in the sheet within the lines thereof at a point intermediate the opposite end of the sheet and the center thereof. said sheet having portions of increased thickness projecting from the. face thereof in the locations in which said thermostats are situated.

21. In a heating pad, a body comprising a sheet of exible rubber, a resistor embedded in said sheet and arranged in convolutions therein extendingtransversely of the sheet, said resistor comprising a low heat section. a heat section of greater heating effect and a common return for said sections, a thermostat connected to one of said sections and embedded in the sheet in the longitudinal median line thereof at a point between the center of the sheet and one end, and another thermostat connected to the other section and embedded in the sheet in the longitudinai median line thereof at a point between the center of thesheet and the opposite end thereof.

22. In a heating pad, a body comprising a thin sheet of elastic plastic material, a resistor embedded in said sheet and comprising a coil of heating wire arranged in convolutions extending across the sheet, said resistor comprising a low heat section, a heat section of vgreater heating effect, and a common return for said sections, a thermostat connected to one of said sections and embedded in the sheet in the longitudinal median line thereof at a point between the center of the sheet and one end, and another thermostat connected to the other section and embedded in the sheet in the longitudinal median line thereof at a point between the center of the sheet and the opposite end thereof, said sheet having shallow bosses with slanting side surfaces projecting from one face thereof and located over the ernbedded thermostats.

23. In a heating pad, a body comprising an elongated thin sheet of exible rubber, a conductor cord connected with said sheet at one end thereof, a resistor embedded in said sheet and comprising helically coiled wire disposed in convolutions extending across the sheet transversely substantially from one end of the sheet to the other end, said resistor comprising a low heat tor-cord-connected end of the sheet substantially to the opposite end thereof, a heating section of greater heating effect extending substantially from said conductor-cord-connected end of the 5 sheet substantially to the opposite end thereof, and a common return for said sections, a thermostat connected to one of said sections and embedded in the sheet in the longitudinal median line thereof at a point between the center of the 10 sheet and the conductor-cord-connected end of the sheet, and another thermostat connected to the other section and embedded in the sheet in the longitudinal median line thereof at a point between the opposite end of the sheet and the 15 center thereof.

24. In a heating pad, the combination with a pad body comprising a thin flexible sheet of rubber, of a resistor of helically coiled wire embedded in the body and arranged in transverse convolua0 tions therein, a conductor cord connected to one end of the body, said resistor comprising a low heat section extending substantially from the conductor-cord-connected end of the sheet to the opposite end thereof, a heat section of great- 23 er heating effect extending from said conductorcord-connected end of the sheet substantially to the opposite end thereof, a thermostat embedded in the sheet toward the end which is remote from the conductor cord, said thermostat being con- 80 nected with one of said heat sections only, another thermostat embedded in the sheet toward the conductor-cord-connected end thereof, said second thermostat being connected with both heat sections, and a common return section leading out of the pad from the last-named thermostat to the conductor cord.

25, In a. heating pad, a body comprising a thin flexible rubber sheet, and a resistor embedded in said sheet and comprising helically coiled wire, 40 said resistor being divided into portions of different heating effect, the turns of the portion of higher heat effect being of less diameter and more r widely spaced than those of the portion of less heating effect.

WALLACE W. DE LANEY. WALTER R.. WEEKS. 

